Serotype patients who are potential candidates for marrow transplantation (malignant disease, genetic disease, and marrow aplasia) and their families to determine genotypic compatibility. Perform mixed leukocyte cultures, cell-mediated lympholysis, neutrophil agglutination, and capillary migration tests on HL-A identical donor recipient pairs who are suitable transplant candidates in order to predict or avoid graft rejection of graft-versus-host disease. Follow postgraft patients by these various means to monitor effectiveness and duration of immunosuppression, and contribute other relevant information to the clinical unit as requested. Obtain and deliver to the National Institute of Allergy and Infectious Diseases serum bank four liters or more of monospecific HL-A antiserum of desired specifications and six liters or more of high-quality duospecific antiserum of desired specificities.